The present invention relates generally to using ultra violet light (UV) for the reduction of fecal coliforms from waste water and specifically to using UV in the 200 to 300 nm wavelength, preferably around 254 nm, to that end.
Conventional gravity fed systems utilize a chlorine contact tank fed by a sand filter to reduce the fecal coliforms. However, such systems are problematic because the chlorine must then be removed from the water. This is accomplished by adding sodium thiosulfate in order to reduce the chlorine count to acceptable levels. However, this has the undesirable effect of lowering the oxygen level in the water to undesirable limits.
The present invention overcomes these disadvantages by using UV to reduce the fecal coliforms instead of chlorine. Generally, the present invention uses UV in approximately the 254 nm range to irradiate waste water.
In one embodiment, a plurality of UV lamps are arranged within a baffle array (creating various irradiation chambers) in a reactor. The arrangement of the baffles causes water to flow in a tortuous path to maximize exposure to the lamps to ensure adequate UV dosages are applied. The flow of water is directed in an inward/outward, up/down, flow pattern as the water is exposed to the UV lamps. Other embodiments depicted in the figures show alternative arrangements of UV lamps and baffles.